The heart supplies oxygenated blood to the body through a network of interconnected, branching arteries starting with the largest artery in the body—the aorta. As shown in the schematic view of the heart and selected arteries in FIG. 1A, the portion of the aorta closest to the heart is divided into three regions: the ascending aorta (where the aorta initially leaves the heart and extends in a superior direction), the aortic arch, and the descending aorta (where the aorta extends in an inferior direction). Three major arteries branch from the aorta along the aortic arch: the brachiocephalic artery, the left common carotid artery, and the left subclavian artery. The brachiocephalic artery extends away from the aortic arch and subsequently divides into the right common carotid artery, which supplies oxygenated blood to the head and neck, and the right subclavian artery, which predominantly supplies blood to the right arm. The left common carotid artery extends away from the aortic arch and supplies the head and neck. The left subclavian artery extends away from the aortic arch and predominantly supplies blood to the left arm. Each of the right common carotid artery and the left common carotid artery subsequently branches into separate internal and external carotid arteries.
During the systole stage of a heartbeat, contraction of the left ventricle forces blood into the ascending aorta that increases the pressure within the arteries (known as systolic blood pressure). The volume of blood ejected from the left ventricle creates a pressure wave—known as a pulse wave—that propagates through the arteries propelling the blood. The pulse wave causes the arteries to dilate, as shown schematically in FIG. 1B. When the left ventricle relaxes (the diastole stage of a heartbeat), the pressure within the arterial system decreases (known as diastolic blood pressure), which allows the arteries to contract.
The difference between the systolic blood pressure and the diastolic blood pressure is the “pulse pressure,” which generally is determined by the magnitude of the contraction force generated by the heart, the heart rate, the peripheral vascular resistance, and diastolic “run-off” (e.g., the blood flowing down the pressure gradient from the arteries to the veins), amongst other factors. High flow organs, such as the brain, are particularly sensitive to excessive pressure and flow pulsatility. To ensure a relatively consistent flow rate to such sensitive organs, the walls of the arterial vessels expand and contract in response to the pressure wave to absorb some of the pulse wave energy. As the vasculature ages, however, the arterial walls lose elasticity, which causes an increase in pulse wave speed and wave reflection through the arterial vasculature. Arterial stiffening impairs the ability of the carotid arteries and other large arteries to expand and dampen flow pulsatility, which results in an increase in systolic pressure and pulse pressure. Accordingly, as the arterial walls stiffen over time, the arteries transmit excessive force into the distal branches of the arterial vasculature.
Research suggests that consistently high systolic pressure, pulse pressure, and/or change in pressure over time (dP/dt) increases the risk of dementia, such as vascular dementia (e.g., an impaired supply of blood to the brain or bleeding within the brain). Without being bound by theory, it is believed that high pulse pressure can be the root cause or an exacerbating factor of vascular dementia and age-related dementia (e.g., Alzheimer's disease). As such, the progression of vascular dementia and age-related dementia (e.g., Alzheimer's disease) may also be affected by the loss of elasticity in the arterial walls and the resulting stress on the cerebral vessels. Alzheimer's Disease, for example, is generally associated with the presence of neuritic plaques and tangles in the brain. Recent studies suggest that increased pulse pressure, increased systolic pressure, and/or an increase in the rate of change of pressure (dP/dt) may, over time, cause microbleeds within the brain that may contribute to the neuritic plaques and tangles. Accordingly, there is a need for improved devices, systems, and methods for treating vascular and/or age-related dementia.